The present invention relates to the field of hydrodynamic bearing assemblies, and more specifically to an improved method for machining the hub and sleeve of a hydrodynamic bearing element.
Hydrodynamic bearings have been the subject of considerable research and development in the past few years. In these types of systems, a lubricating fluid-either gas or liquid-functions as the actual bearing surface between a stationary base or shaft and a rotating sleeve or hub of the motor, or between two such relatively rotating parts. Such bearings have a number of advantages over conventional ball bearings. Such ball bearings, especially when used in motors which are used in disc drives or the like have problems in a number of areas. Specifically, shocks to the disc drive may in turn create a force across the mechanical bearing system which can lead to deformation and damage to the raceway and balls of the ball bearing. Over time, this could result in a failure of the spindle motor to be able to run smoothly and without vibration. Since the spindle motor is directly coupled to the discs, the vibration could easily be directly transferred. A misalignment between the disc which the spindle supports and the transducer which is used to access the surface of the disc could also occur. In either case, the transducer which flies close to the disc surface is more likely to impact the disc.
However, the very fact that a fluid is being used as the bearing surface in a hydrodynamic bearing demands that the bearing must have very fine tolerances for the gap between the shaft and the sleeve, in turn, requiring highly accurate machining of all surfaces. Further, the surfaces must be cleaned of any imperfections which could result in scraping or other damage to the near by facing surface which forms the opposite side of the gap, or in turn the generation of particles. All these goals must be achieved with an economically efficient manufacturing process.
Finally, it is important that provision be made for filling the gap between the shaft and the sleeve. It is important that access be provided to the hydrodynamic bearing gap so that fluid or gas can be inserted into the gap; by the same token, it must be provided that this gap does not diminish the performance of the hydrodynamic bearing, or make it easy for the fluid to leak out of the bearing, or for air to enter the bearing which could diminish the performance of the bearing fluid.
It is therefore an object of the present invention to provide an improved hydrodynamic bearing design and an improved method for fabricating the hydrodynamic bearing.
It is a further objective of the invention to provide a hydrodynamic bearing design which incorporates a filling groove so that oil or other lubricating fluid can be efficiently inserted into the bearing gap without risking the loss of fluid during operation.
It is yet another objective of the invention to provide an improved method for fabricating the hydrodynamic bearing and its oil filling groove so that the efficiency of the manufacturing process is not compromised.
These and other objectives of the invention are achieved in a hydrodynamic bearing assembly including a shaft and surrounding sleeve which define the hydrodynamic bearing gap, the shaft and sleeve defining at the end of the sleeve a flat, radial surface. In forming the bore through the sleeve, which is the outer surface of the hydrodynamic bearing, a boring bar is used having a sharp nose which is used for cutting the interior surface of the bore. The same tool nose, when dragged across a portion of the radial surface at the end of the sleeve forms a groove across this radial surface of the sleeve. The operation may be repeated one or more times, depending on the speed at which the oil is being inserted into the hydrodynamic bearing gap during assembly.
By following this process, the entire boring process is simply achieved without changing the tools which are being used in the boring machine, resulting in an efficient, high speed boring process.